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Title: Homogeneous carbon doping of magnesium diboride by high-temperature, high-pressure synthesis

We have used high-pressure, high-temperature synthesis at 1500–1700 °C and 10 MPa to create homogeneously C-substituted MgB{sub 2} from a B{sub 4}C + Mg mixture. X-ray diffraction analysis showed large peak-shifts consistent with a decrease in the a lattice parameter for the B{sub 4}C-derived MgB{sub 2} as compared to an undoped sample (0.033–0.037 Å, depending on the sample). Microstructural investigation showed a three-phase mixture in the B{sub 4}C-derived ingots: MgB{sub 2−x}C{sub x} (with 0.178 < x < 0.195), MgB{sub 2}C{sub 2}, and Mg. The carbon concentration determined from the lattice parameter shift (5.95 at. %) matched well with the calorimetrically derived concentration of 5.3–5.8 at. % C. Furthermore, the carbon content measured by electron probe micro-analysis was shown to be 6.2 ± 1.3 at. %. Finally, we performed bulk specific heat measurements to determine the homogeneity of C-doping in the MgB{sub 2}. The width of the T{sub c} distribution for the C-doped MgB{sub 2} was only 3–6 K with a full-width half maximum (FWHM) of 1.4 K, compared to a width of 2.5 K and a FWHM of 0.65 for an undoped sample. The consistency of these three measurements on a large-grained homogeneous material is unambiguously supportive of C-substitution.
Authors:
; ; ; ; ;  [1] ;  [2]
  1. Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)
  2. Center for Advanced Materials Characterization in Oregon (CAMCOR), University of Oregon, Eugene, Oregon 97403 (United States)
Publication Date:
OSTI Identifier:
22262545
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 104; Journal Issue: 16; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; BERYLLIUM 6; BORON CARBIDES; CARBON; DOPED MATERIALS; ELECTRON MICROPROBE ANALYSIS; LATTICE PARAMETERS; MAGNESIUM BORIDES; SPECIFIC HEAT; X-RAY DIFFRACTION